Yeah, sort of the same thing here. When I look at the add-on manager, Fast Lane seems to have been installed but no evidence of that in-game or in the launcher. The rest of the add-ons are stuck on "installing".
I've just uninstalled Sims 3, but looking at the add-on manager again, it still shows Fast Lane as installed and the rest of the add-ons are still stuck on "installing." I have tried restarting the app and restarting the computer, and there is no change.
Also, whenever I load this app, my computer's fan goes absolutely nuts, like it wants to take off.
I'm very much not happy with this switchover so far.